1. Field of the Invention
The present invention relates to a load element state detecting device for detecting the state of a load element whose pressure is adjusted by a fluid pressure control circuit, and a fluid pressure control circuit state detecting device for detecting the state of a fluid pressure control circuit.
2. Discussion of Related Arts
There is known a fluid pressure control circuit equipped with an electromagnetic pressure-regulating valve for adjusting the pressure of working fluid such as hydraulic oil or the like supplied in a predetermined flow path by moving a spool, that is, a valve element in accordance with an excitation state of a solenoid driven by a predetermined electrical drive circuit, thereby controlling the pressure of the working fluid supplied to a prescribed load element. As the electromagnetic pressure-regulating valve is known a valve having a feedback chamber into which the output pressure output from the output port is fed back to hold the output pressure to a value corresponding to an drive current representing a instruction value supplied from the electrical drive circuit.
Furthermore, a technique for detecting the state of the fluid pressure control circuit is also known. For example, a 2-phase fluid flow-rate measuring method on the basis of a turbine type flowmeter described in JP-A H8-201130 is known. According to this technique, a turbine is equipped in a flow path in a fluid pressure control circuit, and the rotational speed of the turbine rotated by the flow of the working fluid is detected, so that the flow rate of the working fluid can be calculated on the basis of induced electromotive force being produced in accordance with the rotational speed of the turbine from the predetermined relationship.
For the fluid pressure control circuit disclosed for example in JP-A H10-213215, a hydraulic pressure control circuit is widely used in an automatic transmission for a vehicle. In the vehicle automatic transmission, a clutch and a brake which are hydraulic type friction engaging devices are set as load elements receiving hydraulic pressure adjusted by the hydraulic pressure control circuit, and each of these clutch and brake is equipped with a plurality of frictional engagement elements which are frictionally engaged with one another, and a piston serving as an actuator for engaging these plurality of frictional engaging elements with one another. The piston is moved by the load on the basis of the hydraulic pressure, whereby the plurality of frictional engaging elements are engaged with one another.
As disclosed in JP-A H5-263913, the movement of the piston, that is, the completion of the stroke is judged on the basis of the lapse time from the current supply to the electromagnetic pressure-regulating valve. That is, the time period from the time at which the current is supplied to the electromagnetic pressure-regulating valve until the time when the piston is stroked to a stroke end position is measured and set in advance, and the judgment that the piston stroke has been completed is made on the basis of the fact that the actual current supply time reaches the preset time. As disclosed in JP-A H11-153247, a flow rate of the working fluid is estimated on the basis of a position of a solenoid core detected by a AC component of a drive current supplied to a solenoid valve. As disclosed in JP-A 2001-32863, a pressure rising of the working fluid is detected on the basis of a counter electromotive force induced by a displacement of a solenoid core of a solenoid valve. As disclosed in JP-A 2000-346703, an operational change of a solenoid valve is detected on the basis of a extracted signal through a band pass filter from a drive current in a solenoid core of a solenoid valve.
However, the technique disclosed in Patent Document 4 has a problem that it cannot be adapted to fluctuation in the time needed for the stroke completion which is caused by differences among products or time-lapse variation.
Furthermore, the time needed for the stroke completion is influenced by the viscosity of working fluid or the like, and thus it is necessary to detect the state of the fluid pressure control circuit such as the viscosity of the working fluid in some cases. As described in Patent Document 1, with respect to the state detecting device for the conventional fluid pressure control circuit, a device such as a turbine or the like is required to be equipped in the fluid pressure control circuit and the cost is increased due to the turbine device. In addition, a requirement for a mounting space makes the fluid pressure control circuit large in size, and thus the fluid pressure type mechanical device such as the vehicle automatic transmission or the like employing the fluid pressure control circuit is high in cost and large in size.